#define _CRT_SECURE_NO_WARNINGS 1
#include<stdio.h>
int count(int a)
{
	if (1 == a||2 == a)
	{
		return 1;
	}
	else
	{
		return count(a - 1) + count(a - 2);
	}
	

}
int num(int b)
{
	if (b >= 1)
		return b + num(b - 1);
	else
		return b;
}
int main()
{
	int a = 0;
	scanf("%d", &a);
	int sum = count(a);
	printf("%d", sum);
	return 0;
}